High hardness spheroidal graphite cast iron

ABSTRACT

This invention is characterized in that 1.5 - 6.0% of Ni, 0.2 2.0% of Al and 0.1 - 1.0% of Mo are added to the general spheroidal graphite cast iron. Thus obtained spheroidal graphite cast iron has the following characteristics: it has low hardness in its cast state (as cast) and hence can easily be mechanically worked; the hardness is greatly increased by the subsequent heat treatment; and substantially no deformation is caused with the heat treatment.

Sobue et al.

HIGH HARDNESS SPHEROIDAL GRAPHITE CAST IRON Inventors: Masahisa Sobue, Tokyo; Toshimi Sasaki, Abiko, both of Japan Assignee: Hitachi, Ltd., Japan Filed: Jan. 4, 1974 Appl. No.: 430,762

Foreign Application Priority Data Jan. 12, 1973 Japan 48-5983 U.S. Cl. 75/124; 75/123 CB; 75/123 .1; 75/123 K; 148/35 Int. Cl. C22c 37/10 Field of Search 75/123 CB, 124, 124 J, 75/123 K; 148/35 References Cited UNITED STATES PATENTS 10/1949 Millis 75/123 CB [4 1 Sept. 2, 1975 2,501,059 3/1950 Kluijtmans 75/123 CB 2,516,524 7/1950 Millis 75/123 CB 2,749,238 6/1956 Millis 75/123 CB Primary Examiner-L, Dewayne Rutledge Assistant ExaminerArthur J. Steiner Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT This invention is characterized in that 1.5 6.0% of Ni, 0.2 2.0% of Al and 0.1 1.0% of Mo are added to the general spheroidal graphite cast iron. Thus obtained spheroidal graphite cast iron has the following characteristics: it has low hardness in its cast state (as cast) and hence can easily be mechanically worked; the hardness is greatly increased by the subsequent heat treatment; and substantially no deformation is caused with the heat treatment.

6 Claims, 3 Drawing Figures PATENTED 2|975 3,902,897

FIG.2

HIGH HARDNESS SPHEROIDAL GRAPHITE CAST IRON BACKGROUND OF THE INVENTION This invention relates to a spheroidal graphite cast iron and more particularly it relates to a spheroidal graphite cast iron having a high wear resistance and mechanical workability.

Wear resistance of the usual spheroidal graphite cast iron is improved with increase in hardness. Therefore, conventionally the hardness is increased by induction hardening, oil hardening or water hardening.

However, according to these methods, quenching cracks and strains are apt to be caused because the iron is once heated to a high temperature. Furthermore, in case of high accuracy in size being desired, mechanical working is required after heat treatment and thus the operating steps are increased and the cost becomes higher. Moreover, in many cases, the spheroidal graphite cast iron is cast into products of complicated shapes and it is sometimes impossible to subject these products to said heat treatment.

OBJECT OF THE INVENTION The object of this invention is to provide a spheroidal graphite cast iron which has the following characteristics: the as-cast iron has low hardness and mechanical working can easily be accomplished; subsequently, the hardness is greatly increased by a heat treatment at a relatively low temperature; and deformation caused by heat treatment is very small.

SUMMARY OF THE INVENTION The spheroidal graphite cast iron of this invention comprises, by weight, 2.3 4.2 of C, 1.5 5.0 of Si, not more than 1.0 of Mn, not more than 0.1 of spheroidizing element, 1.5 6.0 preferably about 2.7 of Ni, 0.1 1.0 preferably about 0.5 of M0, 0.1 1.0 preferably 0.5 1.0 of Al and the balance of Fe and incidental impurities.

Furthermore, according to this invention, the cast iron having the above compositions is subjected to tempering treatment.

BRIEF DESCRIPTION OF DRAWING FIG. I and FIG. 2 are rough front and side views which explain the condition of abrasion test carried out in this invention, respectively.

2 FIG. 3 is a drawing which explains measurement of change in size.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples show that according to this invention a spheroidal graphite cast iron which has a low hardness and a high mechanical workability in ascast state, hardness of which is greatly increased by subsequent heat treatment and which shows little deformation caused by heat treatment can be obtained.

Various spheriodal graphite cast irons having compositions as shown in Table 1 were produced by casting in a keel block mold of 30 mm in thickness. Then, test pieces were taken and were subjected to tempering treatment at 500C for 4 hours. The test pieces of the cast irons before subjected to the tempering treatment and after subjected to the tempering treatment were subjected to Brinell hardness test and abrasion test. The results are shown in Table 2. Moreover, changes in size caused by the tempering treatment were measured and the results are shown in Table 2.

Said abrasion test was carried out using the Ogoshi abrasion tester [SeeCo11ection of Articles of Japan Mechanical Society (Vol. 21, pages 555 1955) by Ogoshi et all under the following conditions: load 6.5 kg, abrasion speed 0.5 m/s and abrasion distance 200 m. The test method is as follows: As shown in FIGS. 1 and 2, revolving ring 2 (outer diameter 30 4)) made of sample No. 1 in Table 1 was pressed against a fixed test piece 1 whose wear resistance is to be measured at dried state and it was revolved. Abraded width in the fixed test piece 1 was measured and wear resistance was compared on the basis of this value.

Measurement of changes in size due to the tempering treatment was effected by measuring length L of the test pieces before and after subjected to tempering treatment as shown in FIG. 3 and expressing the change in the length by percentage.

In Table 1, Sample No. 1 is the conventional spheroidal graphite cast irons, comparative samples No. 2 4 are the cast irons containing Ni and either one of A1 or Mo and samples No. 5 17 are the spheroidal graphite east irons of this invention.

Table 1 Chemical Compositions (72) No.

C Si Mn Mg Ni Al Mo Fe 1 3.35 2.50 0.33 0.051 Balance Table 2 Abraded Brinell hardness width 1 (mm) Changes in No. size after After* After* tempering As-cast tempering As-cast tempering (k *50()C X 4 hours It is clear from Table 2 that in case of the conventional spheroidal graphite cast iron No. 1 and No. 2 which had the compositions of No. 1 to which Ni and Al were added, hardness was not increased and rather slightly softened after subjected to tempering treatment. Furthermore, in case of samples No. 3 and 4 which had the compositions of sample No. 1 to which Ni and M0 were added, hardness was only slightly increased. Thus, in case of samples No. 1 4, substantially no change in hardness was caused before and after tempering treatment. Therefore, abraded width hardly changed before and after tempering treatment and no improvement in wear resistance was recognized.

On the other hand, hardnesses of samples No. 5 17 of this invention were all increased after tempering treatment and the abraded width after tempering treatment was reduced as compared with those which were not subjected to the tempering treatment. Thus, it was confirmed that wear resistance was improved. This fact indicates that the spheroidal graphite cast iron of this invention has excellent mechanical workability in as-cast state and has a wear resistance after subjected to tempering treatment. Furthermore, from the fact that the change in length before and after tempering treatment was only a little and could be practically ignored as in Table 2, it was also confirmed that if the cast iron of this invention is previously subjected to finish working after casting, it can be used nearly as it is after tempering treatment.

Therefore, since the spheroidal graphite cast ironof this invention can easily be mechanically worked in ascast state, and the hardness can be increased by the subsequent heat treatment to improve wear resistance. Furthermore, since the change in size caused by the heat treatment is such that may be ignored, the cast iron of this invention can be used as it is as various articles.

Reasons for limitation of the composition ranges of the elements in the spheroidal graphite cast iron of this invention are as follows:

C is essential for forming graphite and when content of C is less than 2.3 castability is lowered and simultaneously carbide is produced and when more than 4.2 strength is decreased. Therefore, content of C is limited to 2.3 4.2 70. Si is an important element which accelerates the graphitization and promotes decrease in eutectic carbon. When content of Si is less than 1.5 it has no graphitization accelerating effect and when more than 5.0 the iron becomes extremely brittle. Therefore, content of Si is limited to 1.5 5.0 When content of Mn which increases the strength exceeds 1.0 graphitization is obstructed and carbide is formed to make the iron brittle. Therefore, content of Mn is limited to not more than 1.0 The spheroidizing element such as Mg 0r Ca is added for spheroidization of graphite and when content thereof is more than 0.1 soundness of castings is damaged. Thus, the content is limited to not more than 0.1 As the spheroidizing elements, any of the known spheroidizing elements, for example, Mg, Ca, Ce, MgCa, MgCe, Mg- CaCe, etc., may be used. When content of Ni which is essential for hardening is less than 1.5 hardening cannot be accomplished and when more than 6.0 martensite is produced in a large amount in as-cast state to result in too high hardeness. Therefore, content of Ni is limited to 1.5 6.0 Al is essential in that it lowers hardness of iron in as-cast state and increases the hardness after heat treatment. When content of Al is less than 0.2 said effects cannot be attained and when more than 2.0 spheroidization of graphite is restrained and fludity of melt is extremely lowered. Therefore, content of A1 is limited to 0.2 2.0 Mo increases hardness after heat treatment and simultaneously shortens the time required for hardening and furthermore, addition of Mo can reduce the amount of Al which lowers fluidity of melt. However, when content of M0 is less than 0.1 the above effects cannot be attained and when more than 1.0 a large amount of carbide is formed in as-cast state to result in too high hardness. Therefore, content of M0 is limited to 0.1 1.0

What is claimed is:

1. A high hardness spheroidal graphite cast iron which consists essentially of, on the basis of weight, 2.3-4.2% of C, 1.5 5.0% of Si, not more than 1.0% of Mn, not more than 0.1% of spheroidizing element, 1.5-6.0% of Ni, 0.2 2.0% of Al, 0.1-1.0% of Mo and the balance Fe and incidental impurities.

2. A spheroidal graphite cast iron according to claim 1, wherein content of Ni is about 2.7 that of Al is 0.5 1.0 and that of M0 is about 0.5

3. A spheroidal graphite cast iron according to claim I, which is subjected to tempering treatment after casting to increase its hardness.

4. A spheroidal graphite cast iron according to claim 3, wherein said tempering treatment is at 500C. for 4 hours.

5. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is Mg. Ca. Ce. Mg-Ca, Mg-Ce. or Mg-Ca-Ce and the amount of said spheroidizing element added is sufficient for spheroidization of graphite.

6. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is Mg and the content of Mg is from 0.048 to not more than 0.1%. 

1. A HIGH HARDNESS SPHEROIDAL GRAPHITE CAST IRON WHICH CONSIST ESSENTIALLY OF, ON THE BASIS WEIGHT, 2,3-4,2% OF C, 1,5 - 5.0% OF SI, NOT MORE THAN 1.0% OF MN, NOT MORE THAN 0.1% OF SPHEROIDIZING ELEMENT. 1,5-6.0% OF NI, 0.2 - 2.0% OF AL, 0.1 - 1.0% OF MO AND THE BALANCE OF FE AND INCIDENTAL IMPURI-TIES
 2. A spheroidal graphite cast iron according to claim 1, wherein content of Ni is about 2.7 %, that of Al is 0.5 - 1.0 % and that of Mo is about 0.5 %.
 3. A spheroidal graphite cast iron according to claim 1, which is subjected to tempering treatment after casting to increase its hardness.
 4. A spheroidal graphite cast iron according to claim 3, wherein said tempering treatment is at 500*C. for 4 hours.
 5. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is Mg, Ca, Ce, Mg-Ca, Mg-Ce, or Mg-Ca-Ce and the amount of said spheroidizing element added is sufficient for spheroidization of graphite.
 6. A spheroidal graphite cast iron according to claim 1, wherein said spheroidizing element is Mg and the content of Mg is from 0.048 to not more than 0.1%. 